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        <a href="./" >autorelease基本使用</a>
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                    <section class="normal" id="section-gitbook_291">
                    
                        <h1 id="autorelease">autorelease基本使用</h1>
<h2 id="">本小节知识点:</h2>
<ol>
<li>【理解】autorelease基本概念</li>
<li>【理解】自动释放池</li>
<li>【理解】autorelease基本使用</li>
</ol>
<hr>
<h2 id="1autorelease">1.autorelease基本概念</h2>
<ul>
<li><p>autorelease是一种支持引用计数的内存管理方式,只要给对象发送一条autorelease消息,会将对象放到一个自动释放池中,当自动释放池被销毁时，会对池子里面的<code>所有对象做一次release操作</code></p>
<ul>
<li><blockquote>
<p>注意,这里只是发送release消息,如果当时的引用计数(reference-counted)依然不为0,则该对象依然不会被释放。</p>
</blockquote>
</li>
</ul>
</li>
<li><p>autorelease方法会返回对象本身</p>
</li>
</ul>
<pre><code class="lang-objc">Person *p = [Person new];
p = [p autorelease];
</code></pre>
<ul>
<li>调用完autorelease方法后，对象的计数器不变</li>
</ul>
<pre><code class="lang-objc">Person *p = [Person new];
p = [p autorelease];
<span class="hljs-built_in">NSLog</span>(<span class="hljs-string">@"count = %lu"</span>, [p retainCount]); <span class="hljs-comment">// 1</span>
</code></pre>
<ul>
<li><p>autorelease的好处</p>
<ul>
<li>不用再关心对象释放的时间</li>
<li>不用再关心什么时候调用release</li>
</ul>
</li>
<li><p>autorelease的原理</p>
<ul>
<li>autorelease实际上只是把对release的调用延迟了,对于每一个autorelease,系统只是把该 Object放入了当前的autorelease pool中,当该pool被释放时,该pool中的所有Object会被调用Release。</li>
</ul>
</li>
</ul>
<hr>
<h2 id="2">2.自动释放池</h2>
<ul>
<li>创建自动释放池格式:</li>
<li>iOS 5.0前</li>
</ul>
<pre><code class="lang-objc"><span class="hljs-built_in">NSAutoreleasePool</span> *pool = [[<span class="hljs-built_in">NSAutoreleasePool</span> alloc] init]; <span class="hljs-comment">// 创建自动释放池</span>
[pool release]; <span class="hljs-comment">// [pool drain]; 销毁自动释放池</span>
</code></pre>
<ul>
<li>iOS 5.0 开始</li>
</ul>
<pre><code class="lang-objc"><span class="hljs-keyword">@autoreleasepool</span>
{ <span class="hljs-comment">//开始代表创建自动释放池</span>

} <span class="hljs-comment">//结束代表销毁自动释放池</span>
</code></pre>
<ul>
<li><p>在iOS程序运行过程中，会创建无数个池子。这些池子都是以栈结构存在（先进后出）</p>
</li>
<li><p>当一个对象调用autorelease方法时，会将这个对象放到栈顶的释放池</p>
</li>
</ul>
<hr>
<h2 id="3autorelease">3.autorelease基本使用</h2>
<pre><code class="lang-objc"><span class="hljs-built_in">NSAutoreleasePool</span> *autoreleasePool = [[<span class="hljs-built_in">NSAutoreleasePool</span> alloc] init];

Person *p = [[[Person alloc] init] autorelease];

[autoreleasePool drain];
</code></pre>
<pre><code class="lang-objc"><span class="hljs-keyword">@autoreleasepool</span>
{ <span class="hljs-comment">// 创建一个自动释放池</span>
        Person *p = [[Person new] autorelease];
} <span class="hljs-comment">// 销毁自动释放池(会给池子中所有对象发送一条release消息)</span>
</code></pre>

                    
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